patch 8.2.1049: Vim9: leaking memory when using continuation line

Problem:    Vim9: leaking memory when using continuation line.
Solution:   Keep a pointer to the continuation line in evalarg_T.  Centralize
            checking for a next command.
diff --git a/src/userfunc.c b/src/userfunc.c
index a27c68d..c6a8a8c 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -3716,7 +3716,7 @@
 
     eap->nextcmd = NULL;
     if ((*arg != NUL && *arg != '|' && *arg != '\n')
-			&& eval0(arg, &rettv, &eap->nextcmd, &evalarg) != FAIL)
+				  && eval0(arg, &rettv, eap, &evalarg) != FAIL)
     {
 	if (!eap->skip)
 	    returning = do_return(eap, FALSE, TRUE, &rettv);
@@ -3773,7 +3773,7 @@
 	// instead to skip to any following command, e.g. for:
 	//   :if 0 | call dict.foo().bar() | endif
 	++emsg_skip;
-	if (eval0(eap->arg, &rettv, &eap->nextcmd, NULL) != FAIL)
+	if (eval0(eap->arg, &rettv, eap, NULL) != FAIL)
 	    clear_tv(&rettv);
 	--emsg_skip;
 	return;